1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a single reel on which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes such as magnetic tapes and the like are used as external recording media for computers and the like. For a recording tape where a large volume of information is recordable and which is wound around a reel, a single reel cartridge whose reel is rotatably accommodated in a compact space is employed.
In such a recording tape cartridge, a reel gear is provided in an annular form at the end surface of a hub of a reel, which hub is shaped as a hollow cylinder having a floor and around which a recording tape is wound between a pair of flanges of the reel. The reel gear is exposed from a gear opening of a case so as to be able to mesh with a driving gear provided at a rotating shaft of a drive device. When the recording tape is to be pulled out from the case and used, in the state in which the reel gear meshes with the driving gear and the reel is positioned in the axial direction, driving force is transmitted to the reel due to the rotation of the rotating shaft such that the reel is driven to rotate.
Positioning of the reel in the axial direction is carried out by the meshing of the reel gear and the driving gear. Specifically, the meshing surfaces of the teeth of the reel gear and the teeth of the driving gear which mesh together are formed in tapered shapes. The reel is positioned in the axial direction in a state in which the respective teeth are meshed together such that there is no backlash therebetween. Therefore, the axial direction reference surface of the reel within the drive device (i.e., at the time when the reel is driven to rotate) is, for example, an imaginary surface which is the meshing pitch surface of the reel gear and the driving gear. Therefore, in a recording tape cartridge equipped with such a reel, the dimensions of the respective portions are determined on the basis of the imaginary reference surface obtained by the meshing together of the reel gear and the driving gear. Thus, designing, and evaluation of the dimensions of the respective portions are complex.
Here, a recording tape cartridge has been conceived of which has a structure in which a reference surface is provided at the end surface of the hub of the reel, separately from the reel gear, and the reel gear does not participate in the function of positioning the reel in the axial direction (see, for example, U.S. Pat. No. 6,273,352). Specifically, three convex portions for reference project at uniform intervals in the peripheral direction from the radial direction outer side portion of the reel gear which is formed in an annular form at the end surface of the hub. The reel is positioned in the axial direction due to references surfaces at the respective convex portions for reference, which are surfaces orthogonal to the axis of the reel, being made to abut a positioning surface of the rotating shaft.
When the reel rotates, there are cases in which the flange, which is at the open end side of the hub opposite the end surface where the reel gear and the like are formed, contacts the recording tape due to wobbling or the like accompanying the rotation of the reel, and force in a direction of pulling the reel gear away from the driving gear is applied to the reel. Further, when the meshing surfaces of the reel gear and the driving gear are formed in tapered shapes as described above, a portion of the torque of the reel is converted, by the tapered surfaces, into thrust in the direction of pulling the reel gear away from the driving gear. Even if these forces are applied, in the state in which the reel gear is used while facing in the direction of gravity (downward), the meshing together of the reel gear and the driving gear is maintained due to the weight of the reel and the recording tape. However, these forces are a cause of destabilizing the rotation of the reel.
Therefore, in the above-described structure disclosed in U.S. Pat. No. 6,273,352, a reel plate, which is formed of a magnetic material, is fixed to the inner side of the reel gear at the end surface of the hub, and the reel plate is attracted and held by a magnet provided at the rotating shaft, without contact between the reel plate and the magnet. The rotation of the reel is stabilized due to this attraction force.
Further, a recording tape cartridge is known which is not provided with a reel plate attracted by a magnet, but in which the reel is urged toward the rotating shaft by a compression coil spring provided within the case (see, for example, U.S. Pat. No. 6,034,850). In this structure, the urging force of the compression coil spring resists force in a direction of pulling the reel gear away from the driving gear, and the rotation of the reel is stabilized. Moreover, at the reel structuring this recording tape cartridge, one of the pair of flanges is provided integrally from the open end of the hub which is formed in the shape of a hollow cylinder having a floor (i.e., is provided from the end portion at the opposite side, in the axial direction, of the end surface where the reel gear and the like are formed), whereas the other flange is attached later to the floor portion side end portion of the hub. In this reel, because the one flange is provided integrally with the open end side of the hub, the hub has high strength (rigidity). Therefore, it can be expected that it is difficult for the hub and the flanges provided at the hub to deform due to the winding pressure of the recording tape or the like, and that wobbling of the flanges which accompanies deformation of the hub is suppressed.
However, it is predicted that, as the recording capacities demanded of recording tape cartridges increase, recording tapes will be made longer and the rotational speeds of reels will be increased, and the times over which reels are driven continuously will be increased. There is therefore the need for reels to be driven to rotate even more stably. To this end, there is still room for improvement in order to rotate a reel more stably.
Further, in the structure disclosed in above-described U.S. Pat. No. 6,034,850, the compression coil spring is disposed between the reel and the case in order to maintain the meshing between the reel gear and the driving gear as described above. Therefore, there is the need to utilize an expensive bearing in order to absorb the relative rotation between the reel and the compression coil spring.